"Minimum" smacks down processing artifacts

[bill t.]

The relatively new "roundness" option in PS CC "Filter->Other->Minimum..." is stated as intended for refining masks.  But it also is a way to reduce destructive processing artifacts on color layers as from over-sharpening, jpegs etc.

The example shows a 100% jpeg crop on the left.  On the right we see the result of the Minimum dialogue set to "Roundess" and a factor of 0.2.  The abundance of halos and edge nastiness is greatly reduced.  The nervous looking original is made gentle and even pretty in the print.  The effects is especially lovable on high contrast transitions that show off the consequences of even mild sharpening.  Even applying new, judicious sharpening is an improvement over the original.

The example shot is not the best.  Oversharpen an image and hit it with "Minimum, 0.2, Roundess."  You may or may not like what you see.

Of course, there are other ways to do this.  But Minimum is quite direct without much fooling around.  The histogram gets a gentle nudge to the left, so you may want to raise it back up with a curves layer.

[mvsoske]

I did wonder about that filter. Thanks for posting the example.  I'll explore it further.

Mark

[Mark D Segal]

Thanks, could be useful to know - in case we receive images that need this kind of treatment. Best of course to the extent we have control over it is not to get ourselves into these nasty artifacts from the get-go.

[Bart_van_der_Wolf]

Thanks, could be useful to know - in case we receive images that need this kind of treatment. Best of course to the extent we have control over it is not to get ourselves into these nasty artifacts from the get-go.

Hi Mark,

I agree, it's an attempt to address over-the-top sharpened files, but IMHO it's a crude one. Much more control is given by blurring an up-sampled version of the file, and then down-sample it back to the original size.

• Step 1. Up-sample to e.g. 300% with bicubic smoother
• Step 2. Apply Gaussian blur, e.g. Radius 1.0
• Step 3. Down-sample to original size with bicubic

The image doesn't get darker as it does with the Minimize filter, and there is more fine control at the sub-pixel level, also to address other artifacts (e.g. Halo).

Of course, for specific JPEG related issues, there are good tools available such as Topaz Labs DeJPEG, which is specifically made to address lossy compression related issues.

Cheers,
Bart

[daws]

...Of course, for specific JPEG related issues, there are good tools available such as Topaz Labs DeJPEG, which is specifically made to address lossy compression related issues.

Agreed -- I've found that Topaz DeJPEG does a great job.

[bill t.]

I really don't see Minimum as useful against jpeg scabs, except for stuff along the edges.

One thing I notice about the Minimum thing is that it creates a rather classic looking, relaxed tonality.  Old Bresson and Eugene Smith prints come to mind.  That's what really struck me about it at first.  Takes off the electronic edge in a unique way.  B&W guys should have a look. 

[TonyW]

The Minimum filter can be very useful to help disguise over sharpening and on its own can often work quite well. 

However I tend to get better results using a technique utilising both the Minimum and Maximum filters.  I believe the technique is called morphological opening.

This seems to offer benefits in restoration of images where there may be a lot of small spots that would be tedious to clone and also can work well with over sharpened images.

Briefly it is applied:
1.   Dup. Background layer
2.   Run Minimum filter at a radius that just removes artefacts (CS6 is limited to whole numbers but seems to work well in most cases – looks like there is more control in CC)
3.   Immediately run the Maximum filter at the same radius.
4.   Change the layer mode to Difference.  This will give an effect very similar to the Find edges filter.
5.   Go to Channels and dup the channel that shows the best contrast and further enhance with levels to make an even higher contrast image
6.   Copy this channel to a new layer
7.   Dup background layer once more and this time apply blur until the artefacts disappear
8.   Select the high contrast edge mask and copy
9.   Paste the copy of the mask onto the blurred copy layer mask.  The image should return to looking the same as the original
10.   Now add a levels adjustment layer and clip it to the blurred background copy with the edge mask.
11.   Adjust the mid tone slider to reveal conceal the artefacting.

Quicker to do than describe but it may be useful.  Happy to give it a try if anyone wants clarification and can post a reasonable size image